Mauro Icardi hit a dramatic late brace to complete his hat-trick but Inter Milan's Europa League hopes were dented in a dramatic nine-goal thriller that saw Fiorentina prevail 5-4 in Florence on Saturday.
Inter travelled to the Artemio Franchi already six points behind Lazio, who occupy fifth position in Serie A and the league's second Europa League qualifying position, and desperate for their first win in five league outings.
But despite responding to Matias Vecino's 23rd minute opener with goals from Ivan Perisic and captain Icardi by the 34th minute, Stefano Pioli's men suffered a dramatic collapse in the space of 17 second-half minutes that saw them concede a penalty and concede three goals before launching a futile, last-gasp revival.
Inter's third defeat in five-game winless run leaves them in seventh place but, less than a year after their takeover by the Chinese Suning group, their hopes of qualifying for Europe's second tier competition are now decidedly compromised.
Inter host Napoli, in third and determined to battle for a top-two finish, next week and Pioli told Sky Sport: "There's no justification for our performance. We had an unexplainable blackout.
"It seems that in this period we just don't know how to respond to certain difficulties. This is a big handicap, because football is full of challenges.
"We have to try to make sure this doesn't happen again."
A week after succumbing to Cristian Zapata's last-gasp leveller for AC Milan in a 2-2 derby draw, an energetic Inter had Fiorentina 'keeper Ciprian Tatarusanu on his toes twice in the opening minutes.
But after a largely dull opening period, it was Paulo Sousa's hosts who took the lead when Matias Vecino was allowed to run in unmarked to smash Hrvoje Milic's cross into the top corner.
Inter completely turned things around in the space of five second-half minutes, Perisic completing a one-two with Candreva to side-foot past Tatarusanu on the half hour.
Five minutes later, Joao Mario's simple through ball found Icardi on the run to smash past Tatarusanu.
Fiorentina had the chance to level minutes after the restart when Khouma Babacar came down under a tug from Danilo D'Ambrosio, but Federico Bernardeschi's woeful chip was parried by Handanovic.
When the Italy midfielder was replaced, to an ironic round of applause and jeers, with Josip Ilicic just before the hour, it sparked a Viola revival that saw Astori beat Handanovic with a powerful header from a corner then Vecino, with his second, give Fiorentina a 3-2 lead on 64 minutes.
Babacar added drama with a late brace in the space of nine minutes, holding off Gary Medel to beat Handanovic with a sublime low shot at his far post before beating the Slovenian from close range when he met Carlos Salcedo's rolled cross nine minutes later.
But against all odds, Icardi produced a stunning late brace, first turning on a sixpence to fire in off the inside of the far post following a cross from the left then nodding home from a corner to complete his hat-trick in the second minute of added-on time.
Vecino later hit out: "We're happy, but we're bitter about how we let them back into it. We can't afford to concede goals like that in a game this important."
Although Fiorentina are one point behind Inter, he added: "Now, we'll try to keep taking aim at Europe. Mathematically, it's still possible. So let's continue in this vein, albeit without the last two minutes."
It set up a dramatic finale that saw Handanovic leave his goal to get involved at a corner, Marcelo Brozovic getting on the end of a poor Fiorentina clearance with a drive that Astori cleared off the line.
Earlier, Atalanta goalkeeper Etrit Berisha pulled off a pair of late saves as the Bergamo side boosted their Europa League hopes with a precious 3-2 win over Bologna to move up to fourth.